The present invention relates to a gas transfer duct, and particularly to a gas transfer duct having a heat-insulating effect and a noise reducing effect suitable for transferring air-conditioning air which is set to have temperature different from room temperature.
A conventional transfer ducts of such a type generally have a structure in which heat-insulating foamed material is spirally wound around an outer circumferential portion of a duct body with no space, and the duct body forms an inner circumferential surface of the duct.
In such a manner, in a conventional duct having a structure in which a duct body forms an inner circumferential surface of the duct, the duct becomes a guide cylinder through which noise generated from an air-blow source such as an air blower is guided to an opening portion of the duct while gas is transferred. The noise is discharged together with the gas so as to give people an unpleasant feeling. There has been a problem that such noise jars on people's nerves because it is generated continuously while the duct is in use, that is, in air-blowing operation.
In order to largely reduce such an unpleasant noise discharged from an opening of a duct to solve the above-mentioned problem belonging to air-blow ducts of a conventional type though it may be impossible to entirely extinguish such an unpleasant noise, there has been developed and proposed one means (see Japanese patent unexamined publication No. Hei. 9-89357) which has such a structure as follows. That is, woven cloth of predetermined width is wound spirally, and then, the connection edges of the cloth are bonded to each other with hard resin strip material, so that an internal surface layer of a duct is formed. A foam strip of open cells is spirally wound on the outer circumferential surface of the woven cloth while adjacent side edges of the foam strip are brought into contact with each other, so that an open-cell foam is formed. A thin film sheet-like strip is spirally wound on the outer circumferential surface of the open-cell foam so as to form an intermediate sheet layer. A foam strip of closed cells is spirally wound on the outer circumferential surface of the intermediate sheet layer so as to form a closed-cell foam. A resin tape is spirally wound on the outermost circumference of the closed-cell foam so as to form an external surface layer which wraps the outermost circumference.
This air-blow duct is a product having a superior effect to be able to show substantially practically perfect effects of noise reducing and heat insulating functions as expected. The duct is therefore an ideal and suitable product for use as an air-blow duct. This product has, however, only one problem that the manufacturing process is complicated and expensive.